I don't think many people have offered actual experiences or examples to underpin the argument that there is a problem.
I have offered experiences and specific examples that indicate it is not a problem, including in games I am playing currently, and people have largely ignored that.
I have personally and directly experienced this problem, and people I know and trust have personally and directly experienced this problem.
Full spellcasters can either completely negate or mostly solve multiple encounters per day, especially
if those encounters are a mix of both combat and non-combat. To then add to this, by your own admission, the idea that a Bladesinger should be very nearly just as good in combat when the Fighter class brings nothing* of its own to non-combat situations is, precisely and exactly, why this thread exists.
Further, you are making a non
-existence claim. That, purely by logic, requires a higher standard of proof. "X can be
a problem in common situations" only requires that you demonstrate that it has
been a problem in a common situation at least once. "X cannot
be a problem in any situation" requires that you prove substantially more. That doesn't mean it's impossible; we can prove that no largest prime number exists, for instance, which is a non-existence claim. In quantifier terms, "X can be a problem" is of the form "there exists an X...", while "X cannot be a problem" is of the form "for all X..." It is harder to prove "for all X..." claims, for the simple reason that they're talking about all
Xs, not just some
Hence: it is bad logic to assert that, because a few finite cases weren't a problem, it is never a problem for anyone. Which is what I said originally. These swans are white, therefore all swans are white.
* As previously stated, universal features granted to all characters equally do not count. So the fact that Fighter gives you two skills is irrelevant, because all
classes do that. Likewise, all characters get a background and a race, so those things are irrelevant for whether the Fighter
gives anything for non-combat.